1. Field of the Invention
The present invention relates to semiconductor devices and fabrication methods thereof, and, more particularly, to semiconductor devices having a contact plug and fabrication methods thereof.
2. Description of the Related Art
Generally, as a semiconductor device becomes more integrated, a low conductive film is created between a dielectric film and a polysilicon film in the conventional metal insulator silicon (MIS) capacitor, and, thus, adequate capacitance may be obtained. Hence, a metal insulator metal (MIM) capacitor may be needed to replace the MIS capacitor.
Typically, an MIM capacitor has an upper electrode and a lower electrode, each of which is formed of a metal film, and a dielectric (conductive) film interposed between the electrodes. The MIM capacitor is formed on a contact plug on a silicon substrate. The contact plug is formed of a TiN film. The contact pug connects the MIM capacitor with a driving transistor to accumulate or discharge electric charge in/from the MIM capacitor.
A contact plug, which enables the MIM capacitor to connect with the silicon substrate, is oxidized when a lower electrode of the MIM capacitor is formed, a dielectric film is deposited or heat processing is performed after deposition of the dielectric film. When the contact plug is oxidized, contact resistance between the MIM capacitor and the silicon substrate increases, or even worse, the MIM capacitor may not be electrically connected with the silicon substrate.
In particular, as the degree of integration of a semiconductor device increases, the size of a contact plug may become smaller. Accordingly, the possibility of contact plug oxidization grows, and hence, a problem of contact resistance, as described above, may become more serious.